There are some four year stretches when a leap year is not observed. A century is not a leap year unless it is divisible by 400. That's why the year 2000 was a leap year and why 2100 is not.
This little factoid got me reading further and that's when I found the "leap second:" an adjustment to time made to coordinate atomic time with the earth's rotation. Atomic time is based on periods/oscillations of the Cesium-133 atom at the ground state (if you want to know more about that, it's easy to look up). The earth is very gradually slowing down (to find out why, that can also be looked up). To keep the clock and the earth in sync, there's the leap second.
Let's say you what to capitalize on a topic of current interest and reinforce information fluency with students. You could have them search for NEXT LEAP SECOND. These happen more often than leap years. And there's another one coming up later this year.
But if you look at the returns from this search in Google, you may see two conflicting reports:
Obviously, these answers don't agree. If searchers don't pay attention to the date information, they could be misled. It's a good opportunity to point out the importance of paying attention to the published date of information.